1. Field of the Invention
The present invention relates generally to communications networks and more particularly to systems and methods for increased data throughput in communications networks.
2. Description of the Prior Art
Demand for multimedia applications, including audio and video data, is rapidly increasing. Some of the more popular uses of multimedia are real-time interactive applications, such as video and audio streaming, Internet Protocol TV (IPTV), transmission of lectures or speeches to a remote audience, and animated simulations. Even when data compression is used, multimedia applications require large amounts of bandwidth.
In an IEEE 802.11 wireless local area network (LAN), broadcast, or multicast packet transmission enables bandwidth-intensive multimedia applications to simultaneously transmit audio and video data packets to each receiving node associated with a group of the wireless LAN. Broadcast packets are transmitted to all receiving nodes of the wireless LAN, whereas multicast packets are transmitted to two or more, but fewer than all, of the receiving nodes of the wireless LAN.
In the wireless LAN, a source node may transmit (e.g., via Ethernet) multicast packets to a multicast-enabled access point, and the access point sends the multicast packets via wireless transmission to destination receiving nodes that have identified themselves as part of the multicast group.
The access point of the wireless LAN may also support unicast packet transmission. For unicast transmission in the wireless LAN, the access point transmits one or more unicast packets to the receiving node identified by an intended destination address included in the unicast packets. After receiving the unicast packet, the receiving node transmits (approximately 9 μs later) an 802.11 acknowledgement (ACK) packet back to the access point. The 802.11 ACK mechanism provides reliable data transmission in the typically highly interfered 802.11 wireless network by confirming to the access point that the unicast packet was received.
A limitation with transmitting multicast packets in the wireless LAN is that the 802.11 ACK does not provide a reliable mechanism for ensuring that the receiving nodes actually received the multicast packets. For example, if the 802.11 access point were to transmit one or more multicast packets to a number of receiving nodes, and each of the receiving nodes were to respond essentially simultaneously with 802.11 ACK packets, the multiple ACK packets received by the access point would comprise “noise” during the period of the multiple simultaneous 802.11 ACKs. To the access point, these multiple simultaneous 802.11 ACKs are undecipherable. This condition may be referred to as a “multiple ACK problem.”
Another limitation with transmitting multicast packets is that the wireless LAN may be limited in the bandwidth used for multicast packets. Because of the multiple ACK problem, the IEEE 802.11 specification for multicast dictates that transmission of multicast packets occur at a minimum allowable physical data rate. Because the receiving nodes may be at various distances from the source of the transmission, and may experience various interference levels, transmitting at the minimum allowable physical data rate improves the probability of reception of the multicast packets by each receiving node. For example, an 802.11 access point transmits multicast packets at a minimum allowable physical data rate of 1 Mbps for 802.11b and 6 Mbps for 802.11a. The receiving nodes do not transmit 802.11 ACK packets to verify reception of the multicast packets. Thus, without the 802.11 ACK mechanism, there is no verification of reception of the multicast packets.
Further, transmitting at the minimum allowable physical data rate under-utilizes available bandwidth in the wireless LAN, which otherwise is capable of supporting much higher data rates. In addition, transmitting at the minimum allowable physical data rate may make the wireless LAN unsuitable for applications that require high rate communication, such as multimedia applications.